Typically, pipe sections which are factory-coated with a parent coating are not fully coated along their entire lengths, but rather are left with uncoated ends to facilitate joining of the pipe section ends (e.g., using a welding process) in the field. The pipe sections are typically welded together as part of the pipe laying process. This welding may take place at the location where the pipe sections are to be reeled, or, such as in the case of sub-sea or offshore pipes, on a lay barge or a reel ship.
Typically, after the field joint is formed, a mold is applied about the field joint and a coating material (usually an insulation material) is injected into the mold at pressure. The interface between the field joint coating and the parent coating may weaken due to flexing or bending of the field joint, and each separate material close to the interface is often the weakest link in the system, and may result in coating failures in this region during bending or flexing of the pipe, particularly in cases where the field joint coating comprises a material that is resistant to flexing, such as injection molded polypropylene.
Similar reference numerals may have been used in different figures to denote similar components.